Conventional output buffers sometimes solve slew rate variation issues by implementing “tuning” capacitors with switchable capacitor banks. The tuning capacitors allow post production tuning. Tuning resistors result in an area and labor penalty, as well as additional calibration circuitry, which add to the overall cost.
Conventional tunable capacitors can be implemented with a bank of switchable capacitors. Depending on the process corners, a certain number of capacitors are switched in or out. Calibration circuitry determines the capacitor variation from the nominal value. In conventional approaches, the switchable capacitor banks need to be implemented as part of the output buffer.
It would be desirable to implement a method to achieve constant slew rate (over process corners) for an output buffer.